There is known a percussive tool comprising a percussion mechanism and a pressure pulser. The percussion mechanism has a hollow housing provided with a working implement. The interior of the housing accommodates for reciprocations therein a piston hammer separating the interior into two chambers of variable volume, particularly a front chamber defined by the working implement, piston hammer and the walls of the housing, and a rear chamber formed by the piston hammer and the walls of the housing. The front chamber continuously communicates with the outside by way of a port made in the housing. A side wall of the housing has an exhaust port provided with a non-return valve, which, depending on the position of the piston hammer may be either blocked by the side surface of the piston hammer or open when the piston hammer contacts the working implement. The non-return valve does not prevent the escape of air from the rear chamber to the outside and blocks the passage of air from the outside into this chamber. The pressure pulser comprises a hollow cylindrical housing having arranged in the interior thereof a fluid displacer in the form of a piston adapted for effecting forced reciprocations therein and forming together with the walls of the housing a working chamber of variable volume, which chamber continuously communicates via a flexible hosepipe with the rear chamber of the percussion mechanism. Arranged in the housing of the pressure pulser is a port for feeding to the working chamber the outside air. This port may, depending on the position of the fluid displacer in the course of forced reciprocations thereof, be either blocked by the side surface of the fluid displacer or it may be open. In order to impart reciprocations to the fluid displacer, the percussive tool has a drive means and a crank mechanism.
When the drive means is engaged, it acts to impart reciprocations through the crank mechanism to the fluid displacer whereby the volume of the working chamber varies according to a certain periodicity. This in turn results in that the rear chamber of the percussion mechanism is subjected to alternating compressions and expansions thanks to the provision of the flexible hosepipe which continuously communicates the rear chamber of the percussion mechanism with the working chamber of the pressure pulser. Pressure in the front chamber of the percussion mechanism is maintained constant and equal to the outside (atmospheric) pressure due to the fact that this chamber continuously communicates with the outside via the port. The piston hammer is caused to move toward the working implement, that is to effect a work stroke, under the action of excess pressure in the rear chamber of the percussion mechanism. When the piston hammer approaches the working implement, or before the piston hammer strikes against the working implement, the exhaust port opens resulting in a pressure drop in this chamber. Subsequent to the collision of the piston hammer with the working implement, an underpressure is produced in the working chamber of the pressure pulser and consequently in the rear chamber of the percussion mechanism. At this instance the outside (atmospheric) pressure prevails over the pressure in the rear chamber which acts to close the non-return valve, while the piston hammer is caused to move in the opposite direction. A further movement of the piston hammer in the opposite direction is decelerated to a complete stop by virtue of an increase in pressure in the rear chamber when the air contained in this chamber is compressed. The air which escapes through the exhaust port after the work stroke is compensated for by a fresh flow sucked in through the port arranged in the housing of the pressure pulser. Thereafter, the heretofore described cycle is recommenced.
Inherent in the above machine is a disadvantage residing in its low specific power, that is the power per unit volume occupied by the percussive tool. This is explained by the fact that the pressure differential between the front and rear chambers of the percussion mechanism is rather small in value. More specifically, it is never in excess of between 0.03 and 0.04 MPa during the return stroke of the piston hammer.
Another disadvantage is that the front chamber of the percussion mechanism is continuously open on the outside and is therefore susceptible to penetration thereinto of foreign, particularly abrasive, particles resulting in excessive wear of parts which may lead to jamming of the piston hammer.
One more disadvantage is the noise caused by the exhaust of compressed air from the rear chamber of the percussion mechanism.
Yet another disadvantage which limits the application of the above percussive tool is that it is usable exclusively in the air medium. Operation of the machine in a loose material or underwater is inherently impossible.
In addition, the machine cannot be adapted for use as a self-propelled withdrawable percussive tool for drilling holes in soils being compacted, since there is no provision for changing the direction of impacts delivered by the piston hammer.